1. The Field of the Invention
The present invention relates to a pressure monitoring device for measuring the pressure that is generated during inflation of a balloon-tipped catheter and the duration of such inflation. More particularly, the present invention relates to a pressure monitoring device having a pressure transducer, a signal converter, and a display device that are substantially encased in a sterilizable housing for repeated use.
2. Relevant Technology
In recent years, balloon-tipped catheters have become increasingly useful in various medical procedures. For example, balloon-tipped catheters have been used to reduce the intrusiveness of medical procedures in various fields of medicine, such as urology, gynecology, cardiology, and the like. Particularly in the treatment of coronary artery disease, the use of balloon-tipped catheters and their associated fluid pressurization systems has become widespread.
Coronary artery disease is the narrowing of the arteries that feed oxygen-rich blood to the heart. The heart needs adequate amounts of oxygen to continually and efficiently pump blood throughout the body. When arteries leading to the heart become narrowed and constricted due to coronary artery disease, several problems can develop. A person with coronary artery disease can experience angina, which is characterized by chest pain or pressure that radiates to the arm or jaw and is caused by a lack of oxygen-rich blood to the heart muscle. If untreated, coronary artery disease can lead to or contribute to heart failure and death.
In recent years, coronary angioplasty has become a common and accepted alternative to the vastly more intrusive coronary bypass surgery. Coronary bypass surgery involves surgical access to the heart, placing the patient on an extracorporeal blood oxygenation system so that the heart can be stopped for surgery, and then surgically attaching one or more passageways by which blood can bypass a clogged coronary artery, all under general anesthesia. Coronary angioplasty, which can be performed using a local anesthetic, involves running a dilation catheter (a catheter having an inflatable balloon near the end) to the diseased artery and then inflating the balloon in order to compress plaque within the artery, thereby obtaining increased blood flow to the heart. Compared to coronary bypass surgery, coronary angioplasty is less intrusive and traumatic, typically involves less risk to the patient, and significantly reduces the patient""s discomfort and recovery time.
During inflation of the balloon during angioplasty, no blood can flow through the artery that is being mechanically dilated. The disruption of blood flow must be limited in duration to about 20 to 60 seconds, so as to avoid tissue damage due to oxygen deprivation. Hence, it is important to carefully monitor the inflation pressure and duration to ensure that blood flow is restored before tissue damage can occur. In most cases, it is not possible to adequately dilate a diseased artery in a single inflation. In cases where it is necessary to undertake multiple inflations in the same artery, it is important to allow sufficient time between successive inflations so that the tissues fed by the diseased artery can become fully oxygenated before blood flow is disrupted again. At the same time, a successful angioplasty procedure requires that the dilation of the artery be conducted for a significant period of time.
In addition to monitoring in real time the inflation pressure and duration, it is also important for the physician performing the angioplasty to have access to historical information regarding the duration and intensity of past inflations and deflations. Accordingly, various devices and gauges have been developed for monitoring inflation and deflation of balloon tipped catheters during angioplasty. All pressure gauges for measuring pressure within a syringe generally have at least two primary components: a pressure sensing unit and a display unit. The pressure sensing unit is positioned to be in fluid communication with the syringe often by being mounted directly thereon. The display unit typically comprises a dial, a liquid crystal display, a graphical device, or another visible system that displays the magnitude of the fluid pressure that is detected by the pressure sensing unit. The pressure sensing unit is connected with the display unit electrically, mechanically, or by other means by which information may be transmitted.
One common pressure gauge is configured with the pressure sensing unit positioned on the syringe, while the display unit is located perhaps several feet away from the syringe. Typically, electrical cables connect the pressure sensing unit with the display unit. It has been found that use of such pressure gauges can be somewhat awkward, since the physician who operates the syringe must repeatedly alternate his or her attention from the syringe to a the display unit or must receive inflation information second-hand from an assistant who monitors the display unit. In addition, the cables and relatively bulky display unit may cause the operating area to become cluttered.
The problems associated with physical separation of the display unit and the pressure sensing unit have been addressed by using integrated pressure gauges in which the pressure sensing unit and the display unit are combined in a self-contained device. Such integrated gauges are generally attached directly to the syringe. Accordingly, an integrated gauge may be more convenient to use, because the operating physician can more exclusively concentrate on the syringe area during the medical procedure. Because integrated gauges are positioned on the syringe in communication with the catheter fluid and relatively near the patient, such gauges must be sterilized for reuse or disposed after the medical procedure. In practice, disposable gauges are often prohibitively expensive, and sterilizable gauges are therefore generally preferred.
Liquid crystal displays (LCD""s) and other mechanisms conventionally used for displaying information measured by digital systems cannot withstand the high temperatures used during sterilization procedures. In addition, a self-contained power supply has not been available in the past that can suitably be used in an integrated pressure gauge and that can withstand sterilization temperatures. While light-emitting diodes (LED""s) would generally be able to withstand sterilization temperatures, their use in a self-contained pressure gauge would be undesirable due to their high energy requirements, which would quickly deplete self-contained energy supplies. Thus, due to the impracticability of using commercially available display devices that can be used with digital pressure gauges, conventional sterilizable integrated pressure gauges have been exclusively analog and mechanical since analog displays consume little or no energy and have no parts that are destroyed by heat sterilization processes.
Integrated mechanical pressure gauges have a sensor diaphragm that may be placed in fluid communication with the syringe, so as to be physically displaced in response to generated fluid pressure. The distance of displacement of the diaphragm is typically proportional to the magnitude of the fluid pressure. The diaphragm may be mechanically connected to a C-shaped flexible metal member, such as a brass or bourdon tube, that is used to mechanically convert the linear displacement of the diaphragm into rotational displacement of a spindle and a pointer across a graduated numerical dial. In this manner, the dial mechanically displays the magnitude of the fluid pressure within the syringe. The integrated pressure gauge is generally removably attached to the syringe such that the gauge may be placed in an autoclave or otherwise sterilized for reuse after each medical procedure.
Sterilizable integrated mechanical pressure gauges of the prior art have experienced a number of problems, however. For instance, the many moving parts within mechanical gauges are relatively delicate and can be easily damaged by mishandling or misuse. For example, if a mechanical pressure gauge is dropped, it can easily be thrown out of calibration by gear teeth being jarred out of alignment or by any of a number of moving parts being broken, dislodged, or bent. In addition, the bourdon tube can be easily damaged and is also subject to fatigue after repeated use. When a bourdon tube experiences fatigue, the pressure gauge in which it is used gives faulty and unreliable readings. Furthermore, mechanical pressure gauges cannot be systematically calibrated to compensate for temperature effects, which can consequently cause inconsistent pressure measurements due to fluctuations in temperature.
Mechanical pressure gauges may also be thrown out of calibration for any of a number of reasons. It is often difficult to reliably or systematically calibrate such mechanical gauges to respond to the effects of prolonged use or simply to ensure that the gauges are xe2x80x9czeroedxe2x80x9d prior to each use. Furthermore, unlike digital pressure gauges, conventional integrated mechanical pressure gauges lack the means for recording and retrieving data relating to past inflation pressures and the duration of past inflations which are generally desirable when performing angioplasty.
In view of the foregoing, it is apparent that it would be an advancement in the art to provide pressure gauges that are less vulnerable to damage from mishandling or misuse than existing integrated, sterilizable gauges.
It would be a further advancement in the art to provide pressure gauges that measure pressure without using a bourdon tube or similar flexible metal member for providing a mechanically driven pressure reading in response to fluid pressure.
It would be another advancement in the art to provide pressure gauges that could be calibrated so as to compensate for temperature affects and to generate reliable measurement readings throughout a range of temperatures.
It would be an advancement in the art to provide integrated and self-contained pressure gauges that utilize an electronic pressure measurement system yet may be removably attached to a syringe and easily and repeatedly sterilized for reuse.
It would be still another advancement in the art to provide integrated and sterilizable pressure gauges which are capable of storing data that relates to past inflation pressures and the duration of past inflations for later retrieval.
It would be another advancement in the art to provide integrated and sterilizable pressure gauges which may be initialized prior to each use to ensure that the gauge is correctly calibrated and will give an accurate and reliable reading.
Such pressure gauges are disclosed and claimed herein.
The present invention relates to pressure gauges for measuring the pressure generated within a balloon-catheter system or in other pressure-generating systems. The pressure gauges of the invention utilize an analog-to-digital-to-analog method of sensing and displaying the generated fluid pressure. Moreover, the magnitude of the fluid pressure is preferably displayed in a mechanical fashion, thereby eliminating the need for liquid crystal displays and light emitting diodes of the prior art.
When the pressure gauges of the invention are used in balloon-catheter systems or other medical applications, they are preferably capable of being sterilized for reuse. Sterilization of the pressure gauge may be facilitated by encapsulating the pressure sensing components within a sterilizable housing, typically comprising stainless steel, and by providing pressure sensing components that are able to withstand elevated sterilization temperatures. Sterilization is conducted, for example, after the pressure gauge has been used with a balloon-tipped catheter in a medical procedure. The pressure gauge is removed from the syringe and is subjected to suitable sterilization procedures, which may include sterilization by thermal means in an autoclave and/or by chemical means.
The pressure gauge includes a transducer, which is preferably a piezoresistive semiconductor transducer, for sensing the fluid pressure that is generated within the syringe. The transducer preferably has a sterilizable diaphragm that is adapted to be in fluid communication with the syringe when the pressure gauge is attached to the syringe. The transducer generates an electrical current that is a function of the magnitude of the generated fluid pressure.
The analog-to-digital function of the pressure gauges is preferably performed by a microprocessor, which converts the electrical current to a series of digital signals. The subsequent digital-to-analog function of the pressure gauges occurs as the digital signals are directed to an analog or mechanical display device, which preferably includes a miniaturized stepper motor. The stepper motor responds to the digital signals by causing a specified angular displacement of a spindle and a pointer across a graduated numerical dial so as to display the magnitude of the generated fluid pressure.
The pressure gauges of the present invention eliminate many of the mechanical or moving components of existing pressure gauges that are sensitive to mishandling or misuse. As a result, the pressure gauges of the invention are less likely to be damaged than prior art devices. In addition, the components of the pressure gauges of the invention are not subject to fatigue during repeated use because there is no bourdon tube or other similar flexible metal member.
Because the pressure gauges disclosed herein include a microprocessor that generates digital signals in response to the fluid pressure in the syringe, the pressure gauge may be adjusted to compensate for temperature effects. The pressure gauge may also be initialized, or xe2x80x9czeroedxe2x80x9d, at the beginning of each use in order to calibrate the system and to provide reliable and accurate measurement readings. The microprocessor may also store in its memory a history of the magnitude and duration of the generated fluid pressure, which is made available for later retrieval. Such pressure history may be retrieved, for example, by causing the pointer on the pressure gauge to indicate past inflation measurements on the dial. Alternatively, pressure history may be displayed by using an infrared emitter exposed on the surface of the sterilizable housing and a corresponding remote receiver unit that displays the past inflation measurements.
The pressure gauges preferably combine several high temperature-resistant components such that the resulting electronic system may withstand the extreme temperatures needed for sterilization, particularly when medical procedures are to be monitored with the pressure gauges. For example, a high temperature-resistant battery is preferably used to generate electrical power for the pressure gauge. In addition, the use of a stepper motor to display the magnitude of the generated fluid pressure on a numerical dial eliminates the need for conventional digital displays that would be damaged during sterilization, such as those that involve liquid crystals. The stepper motor further provides advantages, in that it requires relatively little energy, thereby extending the useful life of the battery and, as a result, the entire pressure gauge.
In view of the foregoing, it is an object and feature of the present invention to provide pressure gauges that are less vulnerable to damage from mishandling or misuse than existing integrated, sterilizable gauges.
It is a further object and feature of the present invention to provide pressure gauges that measure pressure without using a bourdon tube or similar flexible member for providing a mechanically driven pressure reading in response to fluid pressure.
It is another object and feature of the present invention to provide pressure gauges that could be calibrated so as to compensate for temperature effects and to generate reliable measurement readings throughout a range of temperatures.
It is another object and feature of the present invention to provide integrated and self-contained pressure gauges that utilize an electronic pressure measurement system yet may be removably attached to a syringe and easily and repeatedly sterilized for reuse.
It is still another object and feature of the present invention to provide integrated and sterilizable pressure gauges which are capable of storing data that relates to past inflation pressures and the duration of past inflations for later retrieval.
It is another object and feature of the present invention to provide integrated and sterilizable pressure gauges which may be initialized prior to each use to ensure that the gauge is correctly calibrated and will give an accurate and reliable reading.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.